In recent years, advances in technology, as well as ever evolving tastes in style, have led to substantial changes in the design of automobiles. One of the changes involves the power usage and complexity of the various electrical systems within automobiles, particularly alternative fuel vehicles, such as hybrid, electric, and fuel cell vehicles.
Many of the electrical components, including the electric motors used in such vehicles, receive electrical power from alternating current (AC) power supplies. However, the power sources (e.g., batteries) used in such applications provide only direct current (DC) power. Thus, devices known as “power inverters” are used to convert the DC power to AC power, which often utilize several of switches, or transistors, operated at various intervals to convert the DC power to AC power.
In many inverters, the switches have antiparallel diodes connected across each switch to provide a path for the load current (i.e., the motor current) when the switch is off. The transistors and diodes are often implemented using semiconductor devices placed on the same electrical substrate to create an inverter module. The substrate is often made of copper or another conductive material, which also generally has a high thermal conductivity, thereby causing the transistors and diodes packaged together to operate at the same temperature.
Commercially available silicon-carbide diodes are capable of operating efficiently at higher operating temperatures than silicon counterparts. However, most semiconductor transistors or switches are formed from silicon. Because the diodes and transistors are thermally coupled by virtue of their physical proximity and placement on the same electrical substrate, the silicon devices determine the maximum operating temperature for the inverter module and limit the operating temperature of silicon-carbide diodes. Furthermore, the silicon devices require higher surface area electrical substrates in order to avoid exceeding the maximum operating temperature, and also affect the placement of the electrical substrate within the inverter module. Thus, current inverter layouts deprive vehicle power systems of the advantages afforded by silicon-carbide devices.